<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>样式演示</title>
    <style>
        div{
            border: 1px solid red;
        }
        .lift{
            width: 20%;
            float: left;
            height: 300px;
        }
        .center{
             width: 59%;
            float: left;
            height: 350px;
        }
        .right{
            width: 20%;
            float: left;
            height: 300px;
        }
        .footer{
            clear: both;
            text-align: center;
            background: blue;
        }
    </style>
</head>
<body>
<div>第一层</div>
<div>第二层</div>
<div class="lift">第三层左边</div>
<div class="center">第三层中</div>
<div class="right">第三层右</div>
<div class="footer">底层</div>


</body>
</html>